A mathematical model describing this morphology was developed in the 1960s in the United States by Aerospace Medical Research Laboratories in Dayton, Ohio. This model, well known as the Hanavan model, describes parametrically, with respect to given human height and weight, the dimensions of all the parts of the body. Usually, the foot is described as having a sole and toes connected together by means of a joint with a degree of freedom in rotation in a sagittal plane of the foot.
For example, for a 14-year-old adolescent, 1.6 m tall and weighing 50 kg, the foot consists of an assembly of rectangular parallelepipeds. The total length of the foot is 243 mm, the width is 80 mm, the height of the heel is 62 mm and the distance between the back of the foot and the connection of the toes is 207 mm.
Currently, many humanoid robots have been developed, but none of them complies with the Hanavan model. In addition, the known robots have broad and solid feet, either with no mobility or with a passive mobility at the toes. Such feet degrade the fluidity of the gait of the robot and distance it substantially from the way of walking of the human being.
A dynamic calculation shows that to achieve a walk at a speed of 1.2 m/s, still for a robot of 1.6 m and 50 kg, the connection of the foot between sole and toes requires a torque of the order of 20 N·m, with a power of 30 W, and a range of movement from 0° to +60°.